This invention relates to a liquid fuel combustion device of the type in which the gasification of fuel is continued by the heat of combustion produced by the device itself. As a phenomenon peculiar to this type of combustion device, a decreased oxygen concentration necessarily leads to a decreased rate of combustion which, in turn, leads to a decrease in the temperature of combustion exhaust gases. The invention relates to a liquid fuel combustion device designed with attention paid to this point to detect changes in the difference between the combustion exhaust gas temperature and room temperature so as to detect the oxygen-deficient state, thereby stopping the combustion or giving warning.
A conventional liquid fuel combustion device which discharges combustion exhaust gases into the room is liable to cause incomplete combustion as the oxygen concentration in the room decreases, which incomplete combustion, without the user knowing the state, e.g., while he is asleep, may cause carbon monoxide poisoning which, in the worst case, leads to death.
Recently, there have been proposed a device for oxidizing the noxious carbon monoxide to the harmless carbon dioxide with the aid of a catalyst or the like, and a method of detecting deficiency in oxygen by using a flame rod for detection of flame current. In the former, however, the oxygen concentration simply decreases, still involving a possibility of causing carbon monoxide poisoning, while in the latter the flame is liable to flare under the influence of the wind or the like, leading to frequent malfunction; thus, the method is lacking in reliability.
As for combustion devices using gas as fuel, there have been proposed methods including one for detecting deficiency in oxygen by using an element for detecting oxygen partial pressure or oxygen concentration gradient. This element is incorporated in the device such that it is under a high oxygen partial pressure or in a low oxygen concentration atmosphere during normal combustion. More particularly, the element is so set that it is positioned in flame flow during normal combustion and enters the flame which will elongate or lift owing to deficiency in oxygen.
Therefore, it is effective for the complete primary combustion system wherein when the oxygen becomes deficient, the flame elongates so that the oxygen partial pressure or oxygen concentration with respect to the normal operation sharply changes, that is, a condition is established in which it becomes easier to detect changes in oxygen partial pressure and concentration.
In liquid fuel combustion devices using liquid as fuel and particularly liquid fuel combustion devices of the self-heat gasification combustion type in which the gasification of fuel is effected by the heat of combustion produced by the device itself to continue the combustion, such as a stove and pot burner, even if the flame elongates in the case of deficiency in oxygen, such elongation takes place only instantaneously; usually, the flame decreases in size from the normal combustion state, that is, the rate of combustion is decreased. Therefore, if an oxygen change detecting element is provided in a liquid fuel combustion device of such self-heat gasification combustion type in a conventional manner, this will result in detection of the oxygen partial pressure or oxygen concentration gradient in the CO atmosphere downstream of the flame. In the case of an atmosphere-open type in which secondary air is supplied, secondary air migrates into the exhaust gases from downstream of the flame, producing little change in oxygen partial pressure or oxygen concentration gradient, so that it is almost impossible to detect the oxygen-deficient state; thus, it has been difficult to put said means into practical use.